1. Field of the Invention
The present invention relates to a process for producing an aluminum material having an aluminum nitride thin layer on the surface thereof. The aluminum material is suitable for use as an electronics material and acoustic material.
2. Description of the Prior Art
An aluminum material, with an aluminum nitride thin layer formed thereon, is expected to find use as an electronics material and acoustic material, because aluminum nitride has good electrical insulating properties and yet has good thermal conductivity, and because it exhibits a good propagation of sound.
There are several known processes for forming an aluminum nitride layer on an aluminum substrate. They include, for example, the reactive sputtering process, chemical vapor deposition process, and ion implantation process. The first two processes are designed to form an aluminum nitride thin layer on an aluminum substrate by deposition, and the last process is designed to form an aluminum nitride layer in the very thin surface layer of an aluminum substrate by implanting cationized nitrogen into the surface layer of an aluminum substrate. The ion implantation process has many outstanding features. It provides an aluminum nitride layer which has no effect on the dimensional stability of the aluminum substrate and has good adhesion to the aluminum substrate, because it converts the surface layer of the aluminum substrate into an aluminum nitride layer. In addition, it provides an aluminum nitride layer of comparatively high purity if aluminum of adequate purity is employed as the substrate.
Despite the above-mentioned features, the ion implantation process sometimes provides an aluminum nitride layer of poor quality even though aluminum of high purity is selected as a substrate. This is attributable to a trace amount of residual oxygen and carbon dioxide gas in the vacuum chamber which is evacuated to about 1.times.10.sup.-6 Torr for the irradiation of accelerated nitrogen ions. These residual gases get penetrate into aluminum during the process.